The use of sunlight as a heat source is an obvious way to reduce dependency on energy sources such as gas, oil, coal, etc. The solar heating of water is particularly attractive because energy available at one time may be stored for use at a later time. Because energy storage is so convenient, the use of solar energy to heat water is compatible both with the diurnal cycle of the sun and with the intermittent reduction in the availability of sunlight due to clouds.
Another advantage inherent in the use of sunlight to heat water involves the fact that the water need not be heated to high temperatures. Typically, the operating temperature range for a residential or commercial water heating system is between about 130.degree. and about 150.degree. F. Such a temperature range results in relatively high efficiency, and for this reason solar powered water heating systems do not require the use of highly sophisticated thermal collectors.
Realizing the foregoing advantages, numerous attempts have been made heretofore to provide a commercially practical solar powered water heating system. However, none of the prior art systems has achieved real success in the marketplace. Perhaps one reason for this lack of success involves the fact that many of the prior solar powered water heating systems have been unduly complicated. Certainly a major factor in the lack of consumer acceptance of solar powered water heating systems relates to high initial costs. It has been shown that the typical homeowner will not purchase any energy saving device unless it can be demonstrated that the device will pay for itself in energy savings within about three to four years.
The present invention comprises a solar powered fluid heating system which overcomes the foregoing and other disadvantages long since associated with the prior art to provide a system that is uncomplicated in design and therefore low both in initial cost and maintanance costs, and which is readily adapted to effect energy savings of sufficient magnitude to return the initial cost in a minimum period of time. In accordance with the broader aspects of the invention, a solar powered fluid heating system comprises a quantity of refrigerant, a thermal collector for heating and thereby at least partially vaporizing the refrigerant, a separator for separating the vapor component from any liquid component of the heated refrigerant, and a condenser for receiving the vapor component of the heated refrigerant and for transferring heat therefrom to a fluid to be heated. A vapor conduit preferably extends from the thermal collector to the separator and from the separator to the condenser, and a liquid conduit preferably extends from the condenser to the separator and from the separator to the thermal collector. The thermal collector, separator, condenser, vapor conduit, and liquid conduit define a closed refrigerant circuit which contains the refrigerant, and refrigerant pressurizing apparatus is employed to cause the refrigerant to flow through the closed refrigerant circuit. The refrigerant pressurizing apparatus is preferably driven by solar energy, either by means of a plurality of photovoltaic cells or by means of a generator driven by a turbine which is in turn driven by vaporized refrigerant flowing through the vapor conduit from the separator to the condenser. Wind energy may also be used to provide operating power for the refrigerant pressurizing apparatus, either alone or in combination with a solar powered energy source.
In accordance with more specific aspects of the invention, the refrigerant pressurizing apparatus may comprise a pump which receives liquid refrigerant from the condenser and which directs pressurized liquid refrigerant through a portion of the liquid conduit to the separator. Alternatively, the refrigerant pressurizing apparatus may comprise a compressor which receives vaporized refrigerant from the separator and which directs pressurized refrigerant vapor through a portion of the vapor conduit to the condenser. When a compressor is utilized as the refrigerant pressurizing apparatus, a check valve is preferably provided at the outlet of the condenser to prevent refrigerant vapor from entering the liquid conduit. Such a check valve may comprise a chamber for receiving refrigerant flowing from the condenser into the liquid conduit, a ball positioned within the chamber and having a density greater than that of refrigerant vapor and less than that of refrigerant liquid, structure for limiting upward movement of the ball in the chamber when the chamber is filled with refrigerant liquid, and a seat for receiving the ball and thereby preventing the flow of refrigerant out of the chamber when the chamber is filled with refrigerant vapor.
In accordance with other aspects of the invention, the thermal collector preferably comprises first and second flat plates which are spaced apart to define a refrigerant heating chamber therebetween. The first and second plates preferably extend in divergent planes to define a refrigerant receiving zone wherein the plates are spaced relatively close to one another and a refrigerant discharge zone wherein the plates are positioned relatively apart from one another. One or more struts may be mounted within the refrigerant heating zone to prevent both inward and outward movement of the plates relative to each other.
A third plate formed from a thermally insulative material may be mounted within the refrigerant heating zone between the first and second plates. The third plate separates the refrigerant heating zone to an upper refrigerant path extending adjacent the first plate and a lower refrigerant path extending adjacent the second plate. In such instances the first plate is positioned for exposure to sunlight so that refrigerant in the upper refrigerant path is adapted for solar heating. The second plate is exposed to the ambient atmosphere so that refrigerant in the lower refrigerant path is adapted for heating by heat transfer from the atmosphere.
In accordance with yet another aspect of the invention, a secondary refrigerant circuit may be utilized to preheat the refrigerant within the thermal collector. In such instances an evaporator is positioned for exposure to the ambient atmosphere and a condenser is positioned within the refrigerant receiving zone of the thermal collector. The refrigerant in the secondary refrigerant circuit has a substantially lower boiling point than the refrigerant in the primary refrigerant circuit so that even at low temperatures when the sun is not shining, heat is removed from the atmosphere and transferred to the refrigerant in the thermal collector.
A similar secondary refrigerant circuit may be utilized to remove excess heat from the thermal collector during periods when the solar powered water heating system is stagnated. In such instances an evaporator is positioned within the refrigerant discharge zone of the thermal collector and a condenser is positioned for contact with the ambient atmosphere. The refrigerant in the secondary refrigerant circuit has a substantially higher boiling point than the refrigerant utilized in the solar powered fluid heating system. Thus, whenever the temperature of the refrigerant in the thermal collector exceeds the boiling point of the refrigerant in the secondary refrigerant circuit the condenser of the secondary refrigerant circuit is effective to transfer excess heat from the thermal collector to the ambient atmosphere.
Another important aspect of the invention involves the positioning of thermal collector panels, and in those instances in which they are employed, the positioning of photovoltaic cell panels, for maximum exposure to solar radiation throughout the entire day. Preferably, the panels are mounted in an inverted T-shaped array. In this manner the erect panels are positioned for maximum exposure to sunlight at dawn and at dusk, the prone panels are positioned for maximum exposure to sunlight at mid-day, and combinations of panels are positioned for maximum exposure to sunlight at intermediate hours of the day. The outputs of all of the panels are added to provide a combined output which is optimized throughout all of the daylight hours.